1. Field of the Invention
This invention relates to a display unit in which characters, symbols or pictures may be created by the use of lines and columns of graphic display elements moved into visible or invisible positions to create the desired image.
2. Description of the Prior Art
A display unit of this type is taught in German Patent Document DE-OS 31 34 356. This display unit, however, has the disadvantage that it requires two transport belts featuring substantial elasticity in the area where they are bent around the transport rollers in order to form a variable bending radius. This high degree of elasticity required in transport belts is highly undesirable, since they tend to sag due to lack of tension. Also, in the described display unit, spheres are used for display elements.
Using 5.times.7 matrices, 35 spheres are needed for each letter and, with 30 visible characters, and at least 40 more invisible characters (backside and roller area), altogether 70 characters are required. This means that 70.times.35=2450 spheres are required. Such a large number of spheres translates into a large expense for material and also for labor when it comes to inserting the spheres. The required number (2450) of spheres weigh a lot in relation to the transport belt and this unit in turn requires a much stronger belt.
International Patent Specification WO 84/03981 describes a different type of display unit. This unit also features two transport belts which, however, are not mounted above each other but are guided separately over two transport rollers each. The expenditure in this case is even greater than with the previously described prior art display unit.
There are also display units featuring rotating display elements which are arranged in a display area and do not form a display through their presence or absence, but by rotating at 180.degree.. They may have a white surface on one side and a black surface on the other.
This type of display unit is more complicated and expensive than the above described display units because each of these numerous display elements has to be mounted on a rotating axle, requiring high quality bearings which should not be susceptible to corrosion due to condensation. In addition, the cost of manufacturing and assembling these units is quite high.